1. Field of the Invention
The present invention relates to a turbomachine, in particular a turbine or a compressor, and, moreover, to a shroud plate for blades or vanes of a turbomachine of this type.
2. Brief Description of the Related Art
Turbomachines, such as turbines, in particular gas turbines and steam turbines, and also compressors, include a rotor which is mounted rotatably in a fixed stator. Turbomachines of this type are also designated as rotating turbomachines. The rotor in this case usually includes a plurality of moving blade rows which each include a plurality of moving blades. Correspondingly, the stator normally has a plurality of guide vane rows which each include a plurality of guide vanes.
In this context, it is basically known to provide the moving blade rows and/or the guide vane rows with a shroud which has a plurality of shroud portions or shroud plates formed in each case on one of the blades or vanes. The multimembered shroud thus formed possesses an annular arrangement in the mounted state. Within the shroud, the free blade or vane ends of adjacent blades or vanes within the same blade or vane row are supported against one another via the shroud plates. With the aid of shrouds of this type, the axial sealing off and the aerodynamics of the respective blade or vane row can be improved, thus increasing the efficiency of the turbomachine equipped with them. Furthermore, shrouds of this type lead to stabilization via coupling in the form of a mutual circumferential support of large blades or vanes which, because of their radial length, exhibit a certain tendency to oscillate when the turbomachine is in operation.
U.S. Pat. No. 6,616,408 B1 discloses a method for the production of a blade or vane, in which the respective blade or vane is assembled from a plurality of individual parts by means of a high-frequency induction welding operation. A first end part having a blade or vane root and a second end part having a shroud plate are welded to a middle part having the blade or vane profile.
EP 0 285 778 B1 shows a blade or vane which has at its head a shroud plate, that is to say a shroud portion assigned to the blade or vane. In this case, the shroud plate is cast onto the blade or vane head so as to obtain a blade or vane with an integrated shroud plate. For the purpose of better mechanical anchoring between the cast-on shroud plate and the blade or vane, the blade or vane head may have, in the region to be cast around, an undercut contour which is filled during the casting of the shroud plate.
It is known in each case from U.S. Pat. No. 4,538,331 and from U.S. Pat. No. 4,592,120 to produce a rotor portion having integrally a moving blade row by the rotor portion being cast into a casting mold fitted with the moving blades. For this purpose, the moving blades are equipped with a dovetail-like root which projects into the casting mold cavity to be filled and which is embedded into the casting material during the casting of the rotor portion. In this case, a fusion connection occurs between the rotor portion and the respective moving blade.
U.S. Pat. No. 5,113,583 discloses a further method for the production of a rotor portion equipped integrally with moving blades, in which deformable hollow monocrystal blades are arranged, with the exception of a root portion, in a ceramic protective sheath, while, within the framework of an isostatic forging operation, the rotor portion is connected to the root portions of the moving blades by means of a diffusion bonding process taking place at high temperatures and under high pressures.
U.S. Pat. No. 5,904,201 discloses a method for the integral forming of a prolongation on a structural part, such as, for example, a turbine blade. For example, to repair a blade tip, the blade can be dipped from above, with its tip forward, into a melt which preferably includes the alloying material of the blade. In the region of the blade end dipped into the melt, a growth zone is formed, in which the transition between the liquid phase of the melt and the solid phase of the blade takes place. By the blade being drawn slowly out of the melt upward, the blade grows due to the phase transition taking place continuously in the growth zone. To produce a special geometry, ceramic molds may be used, which are arranged in the region of the growth zone.
A further method for the production of an integral prolongation on a structural part, preferably on a turbine blade, is known from U.S. Pat. No. 5,473,322. There, for example for the repair of a blade tip, a ceramic mold is mounted on the blade in the region of the blade tip, in such a way that the blade tip to be prolonged closes off the mold downward while the mold is open upward. The mold is then filled with a melt, preferably consisting of the alloying material of the blade, and a growth zone, in which phase transition takes place, can thereby be formed again in the region of the blade tip. By the blade being lowered slowly or by the mold being raised slowly, the desired growth of the blade can be achieved.
U.S. Pat. No. 6,325,871 B1 discloses a method for the connection of two structural parts formed of superalloy. The structural parts may be two halves of a gas turbine blade which are preferably produced as monocrystals.
U.S. Pat. No. 6,219,916 B1 discloses a method for the production of a rotor portion having integral moving blades. For fastening the individual moving blades, the rotor portion is provided with a linear groove and the moving blade is provided with a root shaped complementarily to the groove. The moving blade can then be connected to the rotor portion by means of linear friction welding.
Insofar as the shrouds are used as axial seals for individual blade rows, they may be exposed to increased wear, with the result that repairs are required. Since the individual shroud plates or shroud portions, which in their entirety form the respective shroud in the mounted state, form an integral part of the associated blade, high repair costs are incurred, since the entire blade has to be repaired and, if appropriate, exchanged.
Furthermore, in the case of moving blades, the individual shroud portions or shroud plates are exposed to extreme centrifugal forces. Moving blades which have an integral shroud plate are under a correspondingly high tensile load, with the result that the service life of the individual moving blade is reduced. The moving blades therefore have to be exchanged earlier.